Several types of sensors generate a voltage or current when excited by an event, including piezoelectric sensors, thermocouples, pressure sensors, and displacement sensors. For example, when a piezoelectric sensor is flexed it generates a voltage that depends on the magnitude of flexing. The voltage generated can be supplied to a circuit that may record data regarding bending, tensile, and compression events sensed by the piezoelectric sensor, as described in the '693 patent and the '059 patent application. Circuits for non-volatile recording of data from an event have needed a source of power, such as may be supplied by a wired source of power or by an energy storage device, such as a capacitor or battery. The energy storage device could be recharged by energy harvesting. For example, piezoelectric devices have been used to harvest energy from a structure subject to strain or vibration, as described in the '693 patent. This energy could then be stored and used to power the circuit for logging data from sensors, processing the data, and transmitting the data.
A circuit that records an event sensed by a sensor using only energy provided by that event was described in the commonly assigned '059 patent application. In this regard, the '059 application describes a system for electronically recording an event that provides mechanical energy to a structure. The system includes the structure and an event sensing and recording node. The event sensing and recording node is mounted on the structure and includes a sensor and a first electronic memory. The sensor includes a device for converting the mechanical energy into an electrical signal. The first electronic memory uses energy derived from the electrical signal for electronically recording the event. All energy for sensing the event and recording the event in the first electronic memory is derived from the mechanical energy. A circuit was also described in that the '059 application that allows for measuring the magnitude of that event. That patent application also provided several uses for the circuit.
As the '059 application noted, “advantageously, the system uses little energy for recording the event and it can harvest that energy from the event itself.” The '059 application also noted that the “event logging circuit [of the '059 application] is self-powered because electricity generated by one of the piezoelectric sensors of [the] array . . . [of the '059 application], as it senses an event, is the electricity used for logging that event in a memory location of [the] event logging circuit . . . . While another source of power may be needed for circuits that read that memory or that take further action based on data in that memory, the event logging circuit itself is self-powered since the event it is detecting is the sole source of energy for operation of the event logging circuit to log the event in its memory. The . . . inventors [of the '059 application] have also found a way to arrange these circuits to provide a self-powered recording indicating the magnitude of the event.”
The present application provides an alternate scheme for using energy from an event sensed by a sensor to power a circuit for recording that event and for measuring its magnitude.